Hydrostatic axial piston machine

ABSTRACT

A hydrostatic axial piston machine of swash plate design includes a pivot cradle configured to be pivoted by a regulating valve. The movement of the pivot cradle is fed back to the regulating valve via a return spring. The return spring is attached to the pivot cradle in the region between its end section on the regulating-valve side and an end section which is remote from the regulating valve.

This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2012 015 503.4, filed on Aug. 4, 2012 in Germany, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

The disclosure relates to a hydrostatic axial piston machine of swash plate design.

An axial piston machine of this type is disclosed, for example, in DE 10 2008 038 435 A1. In said hydrostatic machines, the delivery/displacement volume can be adjusted by pivoting of a pivot cradle, against which a multiplicity of pistons bear which are guided in a cylinder barrel. In the known embodiment, the pivoting of the pivot cradle takes place via a countercylinder and an actuating cylinder, the countercylinder loading the pivot cradle in one direction and the actuating cylinder loading it in the opposite direction. A counterpiston of the countercylinder is loaded with the pump pressure in the usual way, whereas an actuating piston of the actuating cylinder is loaded with control oil via a regulating valve. A valve slide of the regulating valve can be adjusted counter to the force of a return spring, the prestress of said return spring depending on the pivoting angle of the pivot cradle. The valve slide of the regulating valve is situated in its regulating/basic position when the actuating force which acts electrically or electrohydraulically on the valve slide is in equilibrium with the force of the return spring; the pivot cradle is then set to a pivoting angle which is proportional to the actuating force which acts at the regulating valve.

In the known axial piston machine, the return spring is coupled via a linkage to the counterpiston, the regulating valve and the return spring being attached to the housing of the axial piston machine and the linkage protruding out of the housing of the axial piston machine into the attached valve housing.

The attached valve housing with the return spring requires a considerable amount of installation space; in addition, the construction of the housing of the axial piston machine is relatively complex, since the linkage has to be guided through it in a suitable way.

Under the type designation A4CSG, Bosch Rexroth AG presents an axial piston machine with electro-proportional adjustment, the adjustment mechanism of which is described in detail in DE 100 63 526 C1. In this solution, the regulating valve and the countercylinder are likewise coupled mechanically via a driver and are arranged transversely with respect to the axis of a drive shaft which is connected to the cylinder barrel, and are attached to the housing of the axial piston machine. This variant exhibits the same disadvantage as the above-described prior art: as a result of the attachment of the housings for the regulating valve and for the return spring, the radial dimensions of the axial piston machine are comparatively great. In contrast, the disclosure is based on the object of providing a compact hydrostatic axial piston machine.

SUMMARY

This object is achieved by a hydrostatic axial piston machine having the features of the disclosure.

Advantageous developments of the disclosure are the subject matter of the subclaims.

The axial piston machine according to the disclosure is configured with an electro-proportional adjustment of the pivoting angle of a pivot cradle, a counterpiston of a countercylinder and/or an actuating piston of an actuating cylinder acting on said pivot cradle. Said actuating piston can be actuated by means of a proportionally adjustable regulating valve, the valve slide of which is loaded via a return spring with a returning force which is dependent on the pivoting angle. A multiplicity of pistons which are guided in the cylinder barrel which is connected operatively to a drive shaft are supported on the pivot cradle. According to the disclosure, in the region between its end section on the regulating-valve side and the end section which is remote from the regulating valve, the return spring is attached on the pivot cradle. As a result of this geometry, the overall length of the axial piston machine can be reduced considerably, since the attachment usually takes place on the other side of the return spring.

In one preferred exemplary embodiment of the disclosure, the regulating spring is attached indirectly to the pivot cradle.

The regulating spring can be supported, for example, on a spring sleeve, the pivot cradle then being connected to the spring sleeve in a non-positive or positively locking manner by way of a driver.

In an alternative solution, the spring sleeve can be supported on the housing side via a bearing spring.

A very compact solution is obtained if the bearing spring is arranged coaxially with respect to the return spring, it being possible for both springs to lie behind one another.

In order to make sufficient support possible, the spring force of the bearing spring is preferably selected to be greater than the spring force of the return spring.

The overall length of the axial piston machine can be reduced further if the sleeve which supports the return spring has, on the bottom side, a receptacle for an end section of the bearing spring, with the result that both springs overlap one another in sections.

In one exemplary embodiment of the disclosure, the return spring is arranged laterally offset with respect to the actuating cylinder or with respect to the countercylinder.

The orientation of the structural elements can be selected in such a way that the countercylinder, the actuating cylinder and the return spring lie parallel to the drive-device axis.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following text, preferred exemplary embodiments of the disclosure will be explained in greater detail using diagrammatic drawings, in which:

FIG. 1 shows a longitudinal section through a hydrostatic axial piston machine according to the disclosure of swash plate design,

FIG. 2 shows a diagrammatic side view of the open housing of the axial piston machine according to FIG. 1,

FIG. 3 shows an outline sketch of the construction of an adjusting device of a pivot cradle of the axial piston machine according to FIGS. 1 and 2, and

FIG. 4 shows a variant of an adjusting device for a pivot cradle of the axial piston machine.

DETAILED DESCRIPTION

It is presumed in the following comments that the principle construction of an axial piston machine of swash plate design is known, with the result that only the structural elements which are essential for understanding the disclosure will be explained here. Otherwise, reference is made to the specialist literature, for example the prior art which was indicated at the outset.

The axial piston machine 1 has a drive device with a drive shaft 2 and a pivot cradle 4 which is mounted pivotably in the housing. The drive shaft 2 is mounted via antifriction bearings 6 in the housing with a cup-like housing part 8 and a cover 10. The drive shaft 2 is connected fixedly to the cylinder barrel 12 so as to rotate with it, in which cylinder barrel 12 a multiplicity of working pistons 14 are guided displaceably. The latter in each case delimit a working space 16 with a cylinder bore, which working spaces 16 can be brought into a pressure medium connection with high pressure or low pressure via a disk cam. During the rotation of the cylinder barrel 12, the pistons 14 slide with piston shoes 18 on the sliding face of the pivot cradle 4. The adjustment of the delivery/displacement volume and therefore of the piston stroke takes place via an adjusting device 20, the basic construction of which is explained in the prior art described at the outset.

In accordance with said prior art, an adjusting device 20 of this type has a countercylinder 22, the counterpiston 24 of which is connected via a ball joint 26 to the pivot cradle 4. The pump pressure acts in a pressure space 28 of the countercylinder 22, with the result that the end face of the counterpiston 24 is always loaded with pump pressure. In the position which is shown in FIG. 1, the pivot cradle 4 is pivoted out to a maximum value of, for example, +20°, the counterpiston 24 being retracted completely. Here, the counterspring 30 is loaded with a maximum stress. The right-hand end section of the counterspring 30 in FIG. 1 is supported on a spring collar 32 which can be displaced along the counterpiston 24, the displacement path being delimited by a shoulder 34 (see also FIG. 3) on the outer circumference of the counterpiston 24. The other, left-hand end section of the counterspring 30 in FIG. 1 bears against a supporting part 36, the construction of which will be explained later using FIG. 3. As is apparent from FIG. 1, the supporting part 36 for its part is supported on the ball joint 26 and therefore on the pivot cradle 4. The axial spacing between the supporting part 36 and the spring collar 32 when in contact with the shoulder 34 is selected in such a way that the counterspring 30 is loaded with a prestress.

Offset diametrically with respect to the countercylinder 24, an actuating cylinder 38 acts on the pivot cradle 4, the actuating piston 40 of which actuating cylinder 38 delimits an actuating space 42. Merely a proportional magnet 45 of the regulating valve 44 can be seen in the illustration according to FIG. 1. The regulating valve 44 itself is not visible in the section according to FIG. 1 and lies, for example, approximately on the same circumferential circle as the countercylinder 22 below the plane of the drawing in FIG. 1. It goes without saying that the regulating valve 44 can also be positioned in a different way.

Via said regulating valve 44, control oil can be fed to the actuating space 42 or a control oil connection to the tank can be opened in a controlled manner. The actuating piston 40 has a greater diameter than the counterpiston 24. The actuating piston 40 is also connected via a ball joint 46 to the pivot cradle 4. The actuating cylinder 40 is engaged around by an actuating spring 48 which acts on one side via a spring collar 54 on a shoulder 50 and on the other side on a spring collar 52 which for its part is supported via the ball joint 46 on the pivot cradle 4. The axial spacing of the spring collar 52 from the shoulder 50 is in turn selected in such a way that the actuating spring 48 is loaded with a prestress.

In order to set the pivoting angle which is shown in FIG. 1, the pump pressure prevails both in the actuating space 42 and in the pressure space 28, with the result that the pivot cradle 4 is adjusted to its maximum pivoting angle in the manner shown, on account of the greater diameter of the actuating piston 40. As has been explained, the counterpiston 24 is retracted completely in this position of the pivot cradle 4, the spring collar 32 then coming into contact with a shoulder of the housing and rising up from the shoulder 34, with the result that the counterspring 30 is stressed. In principle, the adjustment of the pivoting angle in the direction of a reduction of the delivery/displacement volume takes place by the control oil connection to the tank connector being controlled via the regulating valve 44 and the pivoting taking place accordingly via the resulting moment which acts on the pivot cradle. The desired pivoting angle is maintained when there is an equilibrium of moments.

The essential pressure medium connectors of the pump (tank connector, pressure connector, possibly leakage connector) are formed on the cover 10.

In a greatly diagrammatic manner, FIG. 2 shows a side view of the axial piston machine with the cover 10 removed. The cup-shaped housing part 8 and the cylinder barrel 12 with the working spaces 16 which are delimited by the pistons 14 can be seen. The drive shaft 2 is arranged centrally. Furthermore, the position of the actuating cylinder 38, the countercylinder 20 and the regulating valve 44 is shown. It can be seen from this illustration that the regulating valve 44 is integrated into the housing of the axial piston machine and is not attached on the outside, as in the prior art described at the outset, with the result that the radial dimensions of the axial piston machine can be of very compact configuration. The countercylinder 20 and actuating cylinder 38 lie diametrically opposite one another and act on the indicated pivot cradle 4 which can be pivoted about the pivot axis 56 which runs horizontally in FIG. 2. It can be gathered from the illustration according to FIG. 2 that the axes of the countercylinder 2, the actuating cylinder 38 and the regulating valve 44 are at approximately the same spacing from the axis of the drive shaft 2, that is to say all three structural elements can be integrated into the housing part 8 or the cover 10 which closes the latter.

FIG. 3 shows an outline illustration of part of an adjusting device 20, with the regulating valve 44, via which the actuating space 42 of the actuating cylinder 38 (FIG. 1) can be loaded with control oil, in order to pivot the pivot cradle 4 out of its basic position with a minimum delivery/displacement volume in the direction of the pivoted position (maximum delivery/displacement volume). Here, as indicated using dash—dotted lines in FIG. 3, the maximum pivoting angle a is approximately ±20°. Here, the pivot axis 56 runs perpendicularly with respect to the plane of the drawing in FIG. 3.

As explained, the pivot cradle 4 is mounted in the housing part 8. The regulating valve 44 is received in or on the cover 10 and has a valve slide 58, via which a pressure medium connection between a working connector A, a tank connector T and a pressure connector P which conducts the system pressure can be controlled. The working connector A is in a pressure medium connection with the said actuating space 42 of the actuating cylinder 38. In the basic position of the axial piston machine, the pivot cradle 4 is set, for example, to the pivoting angle indicated in FIG. 3 of −20°. In order to pivot in the direction of minimum delivery/displacement volume (see FIG. 1), control oil is guided via the regulating valve 44 into the actuating space 42 of the actuating cylinder 38, with the result that the pivot cradle 4 pivots back on account of the area difference between the actuating cylinder 38 and the countercylinder 22. The valve slide 58 has a first control edge 60, via which the pressure medium connection between the pressure connector P and the working connector A can be controlled. The pressure medium connection between the tank connector T and the working connector A is controlled via a further control edge 62. In the regulating position of the regulating valve 4 which is shown, the pressure medium connection of the working connector A to the tank connector T and to the pressure connector P is shut off or at least throttled greatly, the working connector A is connected to the tank connector T and the actuating cylinder 38 is correspondingly relieved of pressure in a basic position (not shown) of the regulating valve 44, with the result that the pivot cradle 4 is pivoted back into the starting position (pivoting angle −20°). The regulating position is set when the magnetic force which is applied via a proportional magnet 64 to the valve slide 58 is in equilibrium with the force of a return spring 66 which acts on the valve slide 58 and is coupled to the pivot cradle 4, with the result that the return spring 66 is stressed or relieved depending on the pivoting angle a of the pivot cradle 4. As mentioned, the adjustment of the valve slide 58 takes place via the proportional magnet 64 which acts on the valve slide via a push rod 68. An armature 70 of the proportional magnet 64 is loaded counter to the force of the return spring 66 via a counterspring 72 which for its part is supported on the bottom of a pole tube 74. According to the illustration in FIG. 3, the valve slide 58 projects out of the cover 10, a spring collar 76 being supported on its rounded end section, on which spring collar 76 the return spring 66 acts. The latter is supported for its part on a spring sleeve 78 which is guided displaceably in a housing-side guide 18 such that it can be displaced. In the present case, said guide 18 is formed by a recess of the housing part 8, into which recess the spring sleeve 78 dips, with the result that it is guided with its outer side in the housing. In one variant, the spring sleeve can also be guided on the inside via a guide pin which is fixed to the housing. In the exemplary embodiment which is shown, the spring sleeve 78 has a bottom 82 which is provided with a central aperture, the return spring 66 being supported on the remaining annular shoulder of the bottom 82. The pivot cradle 4 has a driver 84, the end section of which lies approximately in a plane which runs through the pivot axis 56 and is formed perpendicularly with respect to the plane of the drawing in FIG. 1. Said driver 84 has an end section 90 which is connected in a non-positive or positively locking manner to the spring sleeve 78. On account of the pivoting movement, this connection has to be configured in such a way that it permits the pivoting of the pivot cradle 4 and the linear displacement of the spring sleeve 78. In the exemplary embodiment which is shown, a driver recess 88 is formed in the shell of the spring sleeve 78, into which driver recess 88 the ball-like end section 90 of the driver 84 dips, with the result that the pivoting movement of the pivot cradle 4 is converted into a linear displacement of the spring sleeve and the return spring 66 is stressed or relieved in accordance with said displacement. Accordingly, a returning force is generated on the valve slide 58, which returning force is dependent on the pivoting angle a. As has been explained, the regulating valve 44 is situated in its regulating position when approximately the magnetic force and the force of the counterspring 72 correspond to that force which is applied by the return spring 66. That is to say, at the beginning of the actuation the valve slide 58 is first of all extended by the proportional magnet 64 and is then moved back into the regulating position which is shown as the pivoting angle increases.

In this exemplary embodiment, the attachment of the retaining spring 66 to the pivot cradle 4 lies in the region of the plane 86 which contains the pivot axis 56 and is at a considerable distance from the left-hand end section of the retaining spring 66, which end section is remote from the regulating valve 44, with the result that correspondingly the overall length of the axial piston machine is reduced considerably in comparison with the conventional solutions.

FIG. 4 shows a variant of the exemplary embodiment according to FIG. 1, the basic construction of the regulating valve 44 corresponding to that from the exemplary embodiment according to FIG. 3, with the result that reference can be made to the above comments in order to avoid repetitions with regard to the regulating valve 44. The pivot cradle 4 which is shown in FIG. 4 also has a driver 84, the end section 90 of which, which interacts with the spring sleeve 78, lies approximately in the plane 86 which contains the pivot axis 56. Here, however, the end section 90 does not engage into a recess of the spring sleeve 78, but rather engages behind a regulating valve-side annular end face 92 of the spring sleeve 78. In the opposite direction, the latter is loaded by the force of a bearing spring 94 which acts on the bottom 82 of the spring sleeve 78 and is supported on an end face 96 of the guide 80. In the exemplary embodiment according to FIG. 4, a centering pin for the bearing spring 14 is also formed in said end face 96. In order to shorten the axial length further, the bottom 82 has a cup-shaped indentation which forms a receptacle 98 for the sleeve-side end section of the bearing spring 94. The adjacent end section of the return spring 66 dips into the annular space between the outer circumference of the receptacle 98 and the inner circumferential wall of the spring sleeve 78 and is therefore centered by way of the receptacle 98. The bearing spring 94 has a spring force which is greater than that of the return spring 66, with the result that the spring sleeve 78 is prestressed against the end section 90 of the driver 84 of the pivot cradle 4. This exemplary embodiment corresponds functionally to that from FIG. 3, but has the advantage that the assembly is somewhat simpler than in the exemplary embodiment according to FIG. 3, since the end section 90 does not have to be “threaded” into the spring sleeve 78. In the above-described exemplary embodiments, the structural length is reduced virtually by the length of the return spring in comparison with the conventional solutions; the hydrostatic machine according to the disclosure (pump/motor with actuating system) is therefore of considerably shorter construction.

An axial piston machine of swash plate design is disclosed, in which a pivot cradle can be pivoted by means of a regulating valve, the movement of the pivot cradle being coupled back to the regulating valve via a return spring. According to the disclosure, in the region between its end section on the regulating-valve side and an end section which is remote from the regulating valve, the return spring is attached to the pivot cradle.

A hydrostatic axial piston machine according to the disclosure can also be used, in particular, in what are known as hybrid vehicles, for example in a passenger car, having an internal combustion engine and a hydraulic drive train including hydraulic pump, hydraulic accumulators and the two hydraulic motors between the internal combustion engine and an axle. 

What is claimed is:
 1. A hydrostatic axial piston machine of swash plate design, comprising: an adjusting device configured to adjust the pivoting angle of a pivot cradle; one or more of a counterpiston of a countercylinder and an actuating piston of an actuating cylinder configured to act on said pivot cradle, wherein the pivoting angle is configured to be adjusted by a regulating valve, the regulating valve having a valve slide configured to be loaded via a return spring with a returning force that is dependent on the pivoting angle, and wherein the return spring is attached to said pivot cradle in the region between its end section on the regulating-valve side and the end section which is remote from the regulating valve.
 2. The hydrostatic axial piston machine according to claim 1, wherein the return spring is attached indirectly to the pivot cradle.
 3. The hydrostatic axial piston machine according to claim 1, wherein the return spring is supported on a spring sleeve.
 4. The hydrostatic axial piston machine according to claim 3, wherein the pivot cradle is connected to the spring sleeve in a non-positive or positively locking manner by a driver.
 5. The hydrostatic axial piston machine according to claim 4, wherein the spring sleeve is prestressed via a bearing spring in the direction of its bearing position against the driver.
 6. The hydrostatic axial piston machine according to claim 5, wherein the bearing spring is arranged coaxially with respect to the return spring.
 7. The hydrostatic axial piston machine according to claim 6, wherein the return spring and the bearing spring overlap one another in sections.
 8. The hydrostatic axial piston machine according to claim 5, wherein a spring force of the bearing spring is greater than a spring force of the return spring.
 9. The hydrostatic axial piston machine according to claim 5, wherein the spring sleeve has, on the bottom side, a receptacle configured to receive an end section of the return spring.
 10. The hydrostatic axial piston machine according to claim 1, wherein the regulating valve is arranged laterally offset with respect to one or more of the actuating cylinder and the countercylinder.
 11. The hydrostatic axial piston machine according to claim 10, wherein the regulating valve is parallel to the drive device axis. 